Ideal Negative Measurements in Quantum Walks Disprove Theories Based on Classical Trajectories
Abstract
We report on a stringent test of the nonclassicality of the motion of a massive quantum particle, which propagates on a discrete lattice. Measuring temporal correlations of the position of single atoms performing a quantum walk, we observe a 6 σ violation of the Leggett-Garg inequality. Our results rigorously excludes (i.e., falsifies) any explanation of quantum transport based on classical, well-defined trajectories. We use so-called ideal negative measurements—an essential requisite for any genuine Leggett-Garg test—to acquire information about the atom's position, yet avoiding any direct interaction with it. The interaction-free measurement is based on a novel atom transport system, which allows us to directly probe the absence rather than the presence of atoms at a chosen lattice site. Beyond the fundamental aspect of this test, we demonstrate the application of the Leggett-Garg correlation function as a witness of quantum superposition. Here, we employ the witness to discriminate different types of walks spanning from merely classical to wholly quantum dynamics.
- Publication:
-
Physical Review X
- Pub Date:
- January 2015
- DOI:
- Bibcode:
- 2015PhRvX...5a1003R
- Keywords:
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- 03.65.Ta;
- 05.60.Gg;
- 37.10.Jk;
- Foundations of quantum mechanics;
- measurement theory;
- Quantum transport;
- Atoms in optical lattices